Anti-squeal device in disc brake

In a disc brake having a piston, a rotatable disc, and a friction pad having a back plate and urged against one surface of the rotatable disc by said piston, the improvement comprising a plate having a partially spherical projection on one surface thereof abutting the back plate of the friction pad, said piston having a stepped bore therein with a large diameter bore portion facing said back plate and a small diameter bore portion and a shoulder therebetween, said plate being in said large diameter bore portion and a predetermined clearance being left around the circumference of said plate between the large diameter bore portion and the outer circumference of the plate for permitting relative lateral movement between said plate and said large diameter bore portion, a generally flat spacer in said large diameter bore portion having one surface abutting said shoulder and the other surface being substantially flat and opposed to the other surface of said plate for transmitting thrust from the piston to substantially the entire surface of said plate and thence through said plate to said friction pad, a predetermined clearance being left around the circumference of said spacer and said large diameter bore portion for permitting relative lateral movement between said spacer and said large diameter bore portion, and a lubricant between the spacer and the plate.